1. Field of the Invention
The present invention relates to an image stabilizing device for compensating an image blur generated by a vibration applied to said device, and more particularly to a system equipped with an image stabilizing device for optical equipment such as a camera utilizing silver chloride film.
2. Related Background Art
In modern cameras, important operations for phototaking, such as determination of exposure and focusing, are all automated so that the possibility of error in phototaking is very low even for the beginner in camera manipulation, but it has been considered very difficult to automatically prevent the error resulting from camera blur.
In recent years, however, there have been made active research and development for a camera capable of preventing such error in phototaking resulting from the camera blur, particularly that resulting from the vibration of hand of the photographer.
Said hand blur at the phototaking is generally a vibration with a frequency of 1 to 12 Hz, and a basic concept for providing a photograph without image blur even in the presence of such hand blur when the shutter is released consists of detecting the camera blur induced by such hand blur, and displacing a compensating lens according to thus detected value. Therefore, for achieving the above-mentioned object of providing a blur-free photograph even in the presence of a camera blur, it becomes necessary to exactly detect the camera vibration, and to compensate the variation in optical axis induced by the hand blur.
Said vibration (camera blur) can be detected, in principle, by loading the camera with a vibration sensor for detecting the angular acceleration, angular velocity, or angular displacement, and camera blur detection means for electrically or mechanically integrating the output signal of said sensor for generating the angular displacement. The image blur compensation is achieved by driving a compensating optical mechanism for deviating the phototaking optical axis, according to the detected information.
In the following there will be briefly explained an image blur suppressing system (antivibration system) employing an angular displacement detecting device as the vibration sensor, with reference to FIG. 8.
FIG. 8 shows a system for suppressing the image blur resulting from a vertical camera vibration 61p and a horizontal camera vibration 61y, indicated by arrows 61.
In FIG. 8 there are provided a lens barrel 62; angular displacement detecting devices 63p, 63y for respectively detecting the vertical and horizontal angular displacements of the camera in respective directions 64p, 64y; and calculation circuits 65p, 65y for converting the signals from said detecting devices 63p, 63y into drive target signals for a compensating optical mechanism 66 (including drive units 67p, 67y and compensating optical position sensors 68p, 68y), which is driven by said signals to stabilize the image on an image plane 69.
FIG. 9 illustrates an example of said compensating optical mechanism and drive means therefor.
Referring to FIG. 9, a fixing frame 547, supporting a compensating lens 545, is rendered slidable on a pitch slide shaft 549p, across a slide bearing 548p for example of polyacetal (POM) resin. Said frame 547 is pinched between pitch coil springs 551p coaxial with the pitch slide shaft 549p, and is maintained around the neutral position. Said pitch slide shaft 549p is mounted on a first support frame 550.
A pitch coil 552p, mounted on said frame 547, is placed in a magnetic circuit composed of pitch magnets 553p and a pitch yoke 554p, whereby the frame 547 is moved in a pitch direction 546p in response to a current. Said pitch coil 552p is provided with a pitch slit 555p, for detecting the position of the frame 547 in-the pitch direction 546p, in cooperation with a light-emitting element 556p (infrared light-emitting diode) and a photosensor 557p (semiconductor position detector PSD).
On a first support frame 550 there is fitted a slide bearing 548y for example of POM resin, whereby it can slide on a housing 558 on which the yaw slide shaft 549y. Since said housing 558 is mounted on an unrepresented lens barrel, the first support frame 550 is rendered movable in the yaw direction 546y, with respect to said lens barrel. Coaxially with the yaw slide shaft 549y, there are provided yaw coil springs 551y, whereby the housing is maintained about the neutral position, as in case of the frame 547.
Said frame 547 is also provided with a yaw coil 552y, and can also be driven in the yaw direction 546y, in cooperation with yaw magnets 553y positioned on both sides of the yaw coil 552y and a yaw yoke 554y. Said yaw coil 552y is provided with a yaw slit 555y, for detecting the position of the frame 547 in the yaw direction 546y, in a similar manner as in the pitch direction.
Referring to FIG. 9, the outputs of the photosensors 557p, 557y are amplified by amplifiers 559p, 559y and supplied, through various illustrated circuits to be explained later, to the pitch coil 552p and the yaw coil 552y, whereby the frame 547 is driven to vary the outputs of the photosensors 557p, 557y. If the polarities of the coils 552p, 552y are so selected as to reduce the outputs of said photosensors 557p, 557y, there are formed closed loop systems, which are stabilized at points where the outputs of the photosensors 557p, 557y become substantially zero.
There are also provided compensating circuits 560p, 560y for further stabilizing the system shown in FIG. 9; adding circuits 563p, 563y for adding entered instruction signals to the outputs of the amplifiers 559p, 559y, and driver circuits 561p, 561y for generating currents to be supplied to the coils 552p, 552y.
When instruction signals 562p, 562y are given to the above-explained system, the compensating lens 545 is driven in the pitch direction 546p and in the yaw direction 546y, extremely faithfully to said instruction signals.
The above-explained driving method is already known for position control, and said amplifiers 559p, 559y, compensators 560p, 560y and drivers 561p, 561y constitute drive means for the compensating optical mechanism.
FIG. 10 shows the aforementioned drive means for driving the compensating optical mechanism in more details, said means being shown only for the pitch direction 546p.
Current-voltage converting amplifiers 564a, 564b convert photocurrents generated in the photosensor 557p (consisting of resistors R1, R2) by the light from the light-emitting element 556p, and a differential amplifier 565 determines the difference in the outputs of said current-voltage converting amplifiers 564a, 564b. The obtained difference signal represents the position of the compensating lens 545 in the pitch direction 546p. The current-voltage converting amplifiers 564a, 564b, differential amplifier 565 and resistors R3-R10 constitute the amplifier 559p shown in FIG. 9.
An amplifier 566 adds an instruction signal 562p to the difference signal from said differential amplifier 565, and constitutes the adding circuit 563p shown in FIG. 9, in combination with resistors R11-R14. Resistors R15, R16 and a capacitor C1 constitute a known phase advancing circuit, which corresponds to the compensator 560p in FIG. 9, for stabilizing the system.
The output of said adding circuit 563p is supplied, through the compensating circuit 560p, to the driving amplifier 567, which generates a driving signal for the coil 552p, thereby displacing the compensating lens 545. Said driving amplifier 567, resistor R17 and transistors TR1, TR2 constitute the driver circuit 561p in FIG. 9.
An adding amplifier 568 determines the sum of the outputs of the current-voltage converting amplifiers 564a, 564b (namely the total received light amount of the photosensor 557p), and a driving amplifier 569, receiving said sum signal, accordingly drives the light-emitting element 556p. The adding amplifier 568, driving amplifier 569, resistors R18-R22 and a capacitor C2 constitute a driving circuit (not shown in FIG. 9) for the light-emitting element 556p.
The emitted light amount of said light-emitting element 556p varies quite unstably depending for example on the temperature, and the positional sensitivity of the differential amplifier 565 varies accordingly. However such variation can be prevented by controlling the light-emitting element 556p by the above-mentioned driving circuit in the above-mentioned manner that the total received light amount becomes constant.
In the following there will be explained an example of the angular displacement detecting device, employed as said vibration sensor, with reference to FIGS. 11 to 14.
Referring to FIGS. 11 to 14, there are provided a base plate 51 for mounting various components constituting the device; an outer tube 52 provided therein with a chamber enclosing a floating member 53 to be explained later and liquid 54; and a floating member 53 supported by a float supporting member 55, to be explained later, in rotatable manner about a shaft 53a. A projection 53b is provided with a slit-shaped reflective face, and is composed of a permanent magnet, magnetized in the direction of said shaft 53a. Said float member 53 is so constructed as to be balanced in rotation and in floating force about the shaft 53a.
A float supporting member 55 is fixed to the outer tube 52 and supports the floating member 53 through a pivot bearing 56 to be explained later. A square U-shaped yoke 57 mounted on the base plate 51 forms a closed magnetic circuit, in cooperation with the floating member 53. A coil 514 is provided between the floating member 53 and the yoke 57, in fixed relation to the outer tube 52. A light-emitting element (iRED) 58 generates light in response to the current supply and is mounted on the base plate 51. A photosensor PSD, varying the output depending on the position of received light, is mounted on the base plate 51. These light-emitting element 58 and the photosensor 59 constitute optical angular displacement detecting means in which the light is transmitted through a projection (reflecting face) 53b of said floating member 53.
A mask 510 provided in front of the light-emitting element 58 is provided with a slit 510a for passing the light. A stopper member 511, mounted on the outer tube 52, limits the range of rotation of the floating member 53.
The above-mentioned floating member 53 is rotatably supported in the following manner. At the center of the floating member 53, pivots 512 with pointed ends are provided at the upper and lower positions, as shown in FIG. 12 which is a cross-sectional view along a line A--A in FIG. 11. On the other hand, pivot bearings 56 are provided, in mutually opposed manner, at the ends of upper and lower arms of the square U-shaped of said float supporting member 55, and the pointed ends of said pivots 512 are fitted in said pivot bearings, whereby said floating member is supported.
An upper cover 513 of the outer tube 52 is adhered, for example, with known silicon adhesive, thereby sealing the liquid 54 inside the outer tube 52.
In the above-explained configuration, the floating member 53 is formed symmetrically about the rotary axis 53a and is composed of a material of the same specific gravity as that of the liquid 54, so that the floating member 53 does not generate any rotational moment under the influence of gravity in any position, and does not apply any substantial load to the pivot axis. In practice it is not possible to attain zero unbalance, but the error in shape is sufficiently small because the actual unbalance only results from the difference in specific gravity, so that the S/N ratio of friction to the inertia is extremely high.
In such structure, even when the outer tube 52 rotates about the shaft 53a, the internal liquid 54 remains standstill to the absolute space by inertia, so that the floating member 53 does not rotate and there is generated a relative rotation about the rotary axis 53a between the outer tube 52 and the floating member 53. Such relative angular displacement can be detected by the above-mentioned optical detecting means utilizing the light-emitting element 58 and the photosensor 59.
In the above-explained device, the angular displacement is detected in the following manner.
The light from the light-emitting element 58 passes the slit 510a of the mask 510, then irradiates the floating member 53, is reflected by the slit-shaped reflecting face of the projection 53b and reaches the photosensor 59. In this light transmission, said light is formed as a substantially parallel beam by the slit 510a and the slit-shaped reflecting face, whereby a blur-free image is formed on the photosensor 59.
Since the outer tube 52, the light-emitting element 58 and the photosensor 59 are mounted on the base plate 51 and move integrally, the slit image on the photosensor 59 moves by an amount corresponding to the relative angular displacement between the outer tube 52 and the floating member 53. Consequently the output of the photosensor 59, which varies the output according to the position of the received light, corresponds to the positional displacement of said slit image, and the angular displacement of the outer tube 52 can be detected from said output.
As explained before, the floating member 53 is composed of a permanent magnet of the same specific gravity as that of the liquid 54, and such configuration can be attained in the following manner.
When the liquid 54 is composed of inert fluorinated liquid, fine powder of a permanent magnet material, such as ferrite, is mixed as filler into a plastic material, and a specific gravity comparable to that of 1.8 of said liquid can be easily attained around a volume content of 8%. After or simultaneous with the molding of the floating member 53 with such material, it can be magnetized in the direction of said axis 53a, whereby the floating member 53 has the property as a permanent magnet.
FIG. 14 is a cross-sectional view, along a line B--B in FIG. 11, showing the relationship among the floating member 53, the yoke 57 and the coil 514.
As shown in FIG. 14, the floating member 53 is magnetized along its axis 53a, with N and S poles at above and below. The magnetic flux from the N pole passes the square U-shaped yoke 57 and enters the S pole, thus forming a closed magnetic circuit. Thus, if the coil 514 positioned in said circuit is given an electric current from the rear side to the front side of the plane of drawing, said coil 514 receives a force in a direction f, according to Flemming's left hand rule. However, said coil 514 cannot move as it is fixed to the outer tube 52 as explained before, so that a reaction drives the floating member 53 in a direction F. Said reaction is proportional to the current supplied to the coil 514, and is naturally reversed in direction if the direction of the current is reversed. Therefore, the floating member 53 can be arbitrarily driven in this configuration.
The elastic force exerted on the floating member 53 by said driving force is, in principle, to maintain the floating member 53 at a constant position relative to the outer tube 52 (namely moving the two in integral manner). Therefore, if said elastic force is strong, the outer tube 52 and the floating member 53 move integrally, so that the desired angular displacement is not generated. However, if said driving (elastic) force is sufficiently smaller than the inertia of the floating member 53, there can be obtained a response even to an angular displacement of a relatively low frequency.
FIG. 15 shows an electrical circuit of the angular displacement detecting device explained above.
Current-voltage converting amplifiers 515a, 515b (and resistors R33-R36) convert the photocurrents 517a, 517b generated in the photosensor 59 by the reflected light 516 from the light-emitting element 58 into voltages, and a differential amplifier 518 (and resistors R37-R40) the difference in the outputs of said current-voltage converting amplifiers 515a, 515b, namely the angular displacement (relative angular movement between the outer tube 52 and the floating member 53). The output thus obtained is divided by resistors 519a, 519b to obtain an extremely small output, which is supplied to a driving amplifier 520 (and a resistor R41 and transistors TR11, TR12) for supplying a current to the coil 514. By effecting a negative feedback (the wiring to the coil 514 and the direction of magnetization of the floating member 53 being so selected that the floating member 53 returns to the center position in response to the output of a differential amplifier 518), there is generated an elastic force (driving force) sufficiently smaller than the inertia of the floating member 53 as explained above.
An adding amplifier (and resistors R42-R45) obtains the sum of the outputs of said amplifiers 515a, 515b (corresponding to the total amount of the reflected light 516 received by the photosensor), and the obtained sum is supplied to a driving amplifier 522 (and resistors R47-R48, a transistor TR13 and a capacitor C11) for activating the light-emitting element 58.
Although the light emission of the light-emitting element 58 varies quite unstably depending on the temperature, the above-explained driving method of said element according to the total amount of received light provides an always constant total photocurrent from the photosensor 59, so that the detection sensitivity of the differential amplifier for the angular displacement becomes extremely stable.
FIG. 16 shows the structure of a servo angular acceleration sensor, representing another example of the vibration sensor.
An outer frame bottom member 523 is integrally fixed to a support member 524 and bearings 525a, 525b of low friction, such as ball bearings, which support the both ends of a shaft 526. Said shaft 526 rotatably supports a seesaw 528 equipped with coils 527a, 527b.
Above and below said coils 527a, 527b and seesaw 528, and spaced therefrom, there provided magnetic circuit plates 530a, 530b constituting cover members and permanent magnets 531a, 531b, 532a, 532b in mutually opposed manner. As mentioned above, the magnetic circuit plates 530a, 530b also serve as cover members for the outer frame. Said permanent magnets 531a, 531b, 532a, 532b are mounted on magnetic circuit rear plates 533a, 533b which are fixed at the bottom of the outer frame 523.
On the coil 527a of said seesaw 528, there is provided a slit plate 534 provided with a slit 534a penetrating in the direction of thickness. The magnetic circuit plate 530a, positioned above said slit 534a and serving as the cover member of the outer frame, is equipped with a photoelectric displacement measuring device 535 such as a SPC (separate photodiode), while the magnetic circuit rear plate 533a, positioned below the slit 534a, is equipped with a light-emitting element 536 such as an infrared light-emitting diode.
In the above-explained structure, when an angular acceleration a is applied to the outer frame as indicated by an arrow 537, the seesaw 528 is inclined in relative manner in a direction opposite to said angular acceleration a, and the angle of said inclination can be detected by the position, on the displacement measuring device 535, of a light beam emitted from the light-emitting element 536 and transmitted by the slit 534a.
The magnetic fluxes from said permanent magnets 531a, 531b pass the coils 527a, 527b, magnetic circuit plates 530a, 530b, and coils 527a, 527b again to reach the permanent magnets 532a, 532b, while those from said magnets 532a, 532b pass the magnetic circuit rear plates 533a, 533b and return to said magnets, whereby closed magnetic circuits are formed, with magnetic fluxes running perpendicularly to the coils 527a, 527b. Therefore, by a control current given to the coils 527a, 527b, the seesaw 528 can be driven along or opposite to the direction of said angular acceleration a.
FIG. 17 shows an example of the angular acceleration detecting circuit, to be employed in the servo angular acceleration sensor of the above-explained configuration.
Said circuit consists of a serial connection of a displacement detecting amplifier 538 for amplifying the output from the above-mentioned detector 535, a compensating circuit 539 for stabilizing the feedback system, a driver circuit 540 for current amplification of the amplified output from said detecting amplifier 538, for supply to the coils 527a, 527b, and said coils 527a, 527b.
In this example, the winding direction of said coils 527a, 527b and the direction of polarity of the permanent magnets 531a, 531b, 532a, 532b are so selected that a force is generated in a direction opposite to the rotating direction of the seesaw 528 under the external angular acceleration a when said coils 527a, 527b are energized.
The servo angular acceleration sensor of the above-explained configuration functions in the following manner. When an angular acceleration a is applied to said sensor as shown in FIG. 16, the seesaw 528 rotates, by inertia, in the opposite direction relative to the outer frame, whereby the slit 534a, provided on said seesaw 528, moves in a direction L. Consequently the center of the light beam entering the detector 535 from the light-emitting element 536 is displaced, and the detector 535 generates an output proportional to the amount of said displacement.
Said output is amplified in the displacement detecting amplifier 538, then subjected to current amplification in the driver circuit 540 after passing the compensating circuit, and supplied to the coils 527a, 527b.
When the coils 527a, 527b are given a control current as explained above, the seesaw 528 is given a force in a direction R, which is opposite to the direction L of the external angular acceleration a, and said control current is regulated in such a manner that the light beam entering the displacement detector 535 returns to the initial position in the absence of said external angular acceleration a.
The control current in said coils 527a, 527b is proportional to the rotating force applied to the seesaw 528, and said rotating force is proportional to the force required to return said seesaw to its original position, or to the magnitude of the external angular acceleration a. Consequently the angular acceleration a, required as control information for example in the image blur suppressing system of a camera, can be obtained by said control current, read as a voltage V across a resistor 541.
FIG. 18 is a more detailed circuit diagram of the angular acceleration detecting circuit shown in FIG. 17.
In the circuit shown in FIG. 18, an amplifier 538a and resistors 538b, 538c correspond to the displacement detecting amplifier 538 in FIG. 17, and effect detection of position, by amplification, with conversion to voltage, of the photocurrent from the displacement detector 535. A capacitor 539a and resistors 539b, 539c correspond to the compensating circuit 539, while a driving amplifier 540a, transistors 540b, 540c and resistors 540d, 540e, 540f correspond to the driver circuit 540 for driving the coils 527a, 527b.
A camera is usually provided with a function of light metering and a function of date recording, and it is already known that, if these functions are executed in consideration of the camera position (whether the photographer holds the camera in horizontal or vertical position), there can be obtained a more accurate result (in case of-light metering) or a more comfortably observable photograph (in case of date recording). More specifically, for example, the date recording matching the direction of the photographed object can be achieved by recording the date in the lower part of the image frame along the longer side thereof when the camera is held in the horizontal position, and in the lower part along the shorter side when the camera is held in the vertical position.
For realizing such function, the camera has to be equipped with means for detecting the position of the camera (namely means for detecting the direction of gravity), but the camera will inevitably become bulky and expensive if it is equipped with the above-explained antivibration system, in addition to such position detecting means.